/Engine/Plugins/Experimental/Water/Source/Runtime/Public/WaterMeshComponent.h
Use this instead of GetMaterialRelevance, since this one will go over all materials from all tiles
[FMaterialRelevance](API\Runtime\Engine\Materials\FMaterialRelevance) GetWaterMaterialRelevance ( [ERHIFeatureLevel::Type](API\Runtime\RHI\ERHIFeatureLevel__Type) InFeatureLevel ) const